1. Field of the Invention
The invention relates to a method of producing a chalcogenide semiconductor layer of the ABC2 type with optical process monitoring, wherein the developing layer is irradiated with light during its production, the light reflected from the layer is detected and the received light signal is assigned to characteristic points of the layer production.
2. The Prior Art
U.S. Pat. No. 5,725,671 discloses an apparatus for producing a thin layer of ABC2 chalcopyrite which, in addition to a substrate support and means for providing the elements A (Cu or Ag), B (In, Ga or Al) and C (S, Se or Te) also provides means for monitoring/presenting the physical properties of the developing layer over time. During production of the chalcopyrite thin layer of the ABC2 type, the materials A, B and C, in a first step, are deposited simultaneously deposited on a substrate and, in a second step, either a gas with elements B and C or a gas with elements A, B and C, with B being present in excess, reacts with the thin layer applied during the first step. At the same time, an optical process control is performed in order to define the terminal point of the second step about a specific change of the physical properties of the developing layer. For this purpose, the developing chalcogenide layer (among others) is irradiated with IR light and the light reflected from the surface of this layer is measured in dependency of time. The terminal point of the production process results from the interval of 5 to 15 minutes' time following the last abrupt change of the signal. However, no provision has been made directly to deduce the terminal point of the production process from a signature of the measured light.
The production of polycrystalline chalcogenide semiconductor layers by means of a chalcogenation of individual/successively deposited metallic precursor layers is generally known from the prior art (described, for instance, in Thin Film Cells and Technologies; 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, 6-10 Jul. 1993, Vienna, Austria, pp. 537-540). The sulfurizing/chalcogenizing process takes place in a lamp furnace or in a thermally heated furnace and may take only a very short time. Technologically conditioned variations of the properties of the precursor layers and of the process parameters may lead to deviations in the process sequence and in most cases necessitate a change in its sequence. Hitherto, it has not been possible to control the last-mentioned process in dependence of the physical properties of the developing chalcogenide layer.